The disclosed invention relates to a novel unitized check valve which is particularly adapted for use with corrosive fluids and for being used in corrosive environments. Check valves may be subjected to exposure by corrosive media when utilized as a component of a reciprocating pump or when installed in-line in a piping system. Other uses and installations of check valves are well known and the present invention is not limited solely to use in corrosive media.
Stem-guided unitized check valves have been used in reciprocating pumps. Typically, the valve disk is guided by the stud and a sleeve. The sleeve is fastened to the valve seat and to the spring which biases the disk. Usually, the seat is webbed in order to provide a base for the stud. These check valves have been commercialy successful but continue to suffer from several disadvantages. Firstly, the valve seat is retained in the fluid end of the pump in a tapered bore. The webbed seat varies in flexibility around its circumference so that there are tight and loose spots in the fit with the result that fluid washouts may occur. Secondly, a webbed seat has a larger wetted perimeter than an open bore seat with the result that the webbed seat has a greater pressure drop and therefore operates less efficiently than an open bore seat. Finally, the valve assembly requires threaded fastening. Threaded fastening is undesirable because the threads cannot tolerate much metal loss before their strength is compromised. Corrosion resistant threads, on the other hand, are subject to galling. Additionally, threads require machine operations and thereby added expense.
Blackford, U.S. Pat. No. 2,649,277, discloses a check valve wherein a guard comprised of a resilient material is removably connected to the closure disk by the seating of pendent legs in a circumferential groove. The legs are angularly movable to permit the foot projections thereof to be received within or to be removed from the groove. The guard is made from a resilient material which therefore may not be able to withstand the temperature extremes and fluctuations of the corrosive fluid. The patent discloses that the valve components are threaded together, a feature which is undesirable with corrosive fluids and media. The reference fails to disclose that the disk is bottom guided. Blackford et al, U.S. Pat. No. 2,710,023, is another attempt to provide an interlocking between the components of the valve.
Richardson, U.S. Pat. No. 1,959,644 and Butlin, U.S. Pat. No. 2,904,065, disclose valve assemblies wherein the retainer is snap-fit into engagement with the valve body. Such a snap-fit is undesirable, particularly when the valve is comprised of hard, inflexible materials.
It can be seen, therefore, that a unitized check valve which may be easily and quickly assembled and disassembled is advantageous for those situations wherein the valve is subject to corrosive media. The components of the check valve are, preferably, comprised of stainless steel or other similar hard inflexible corrosion-resistant materials able to withstand the severe temperature fluctuations normal for such environments. The valve should not require the use of threads because of the problem of galling and/or metal loss. Furthermore, press fit connections must be avoided because of the materials of construction. The valve should be easily and quickly assembled and disassembled with the mere turn of a hand or of a wrench because of the tight confines in which the valve is frequently used.